1. Field of the Invention
The field of the invention relates to an apparatus and a method for using the apparatus for the measurement and/or transfer of a fixed volume of liquid sample.
2. Description of the Related Art
General methods to determine o-phthalaldehyde (OPA) or glutaraldehyde concentrations are mainly instrumental measurements that could be classified into chromatographic measurement (chromatographic, HPLC analysis) or non-chromatographic measurement (direct spectroscopic assay). For HPLC analysis, OPA or glutaraldehyde are measured by both a derivative method or a non-derivative method. The most common derivative method is to convert OPA or glutaraldehyde to 2,4-dinotrophenylhydrazones by reacting OPA with 2,4-dinitrophenylhydrazine. Since the UV absorption is greatly enhanced, this method is valuable for low level OPA or glutaraldehyde measurements especially in environmental analysis. For measurements of high concentrations of OPA or glutaraldehyde, such as the OPA or glutaraldehyde disinfectants, OPA or glutaraldehyde could be measured directly without making derivatives first. OPA or glutaraldehyde may be analyzed easily with GC analysis. For non-chromatographic analysis, OPA or glutaraldehyde could be measured directly with spectrophotometric methods. However, one drawback to this method is that there must be no interference at the specific wavelength used. For example, OPA or glutaraldehyde could be oxidized slowly by air and the carboxylic acid formed may interfere in such assays.
All three instrumental methods involve the preparation of samples and use of an instrument. They are all time-consuming and too expensive or too complicated for hospital end users. Therefore, Albert Browne and 3M have developed a simple strip procedure for a Pass/Fail test. In such a test, the strip was dipped into either OPA or glutaraldehyde solutions for a certain amount of time. After a predetermined time, the strip color was compared with some standard colors. Their strip chemistry principles were not released. The problems with this method are consistency and accuracy. The strip method has the following problems (1). Good solutions (OPA or glutaraldehyde higher than xe2x80x9cPOIxe2x80x9d, the point of interest) often fail the test for different reasons. (2). The soaking time and waiting time have to be controlled carefully. Any deviation will lead to different shades of color and a false reading. (3). Moving of the strip when soaking will lead to the loss of chemical reagents to the OPA or glutaraldehyde solutions leading to false reading. (4). Individual users have different color recognition habits and often have a different opinion of the end-color. (5). The final color is dependent on many factors and is particularly sensitive to time.
The current invention provides another method without the above problems. Although the chemistry principle could also be used for the strip approach, in a preferred embodiment it is used for the color change of a solution.
The present invention pertain to a liquid measuring device that measures a fixed volume of liquid including a first barrel having a proximal and distal end and a gas or vapor permeable but liquid impermeable barrier situated in the barrel between the proximal and distal ends, whereby the liquid can only be filled up to the barrier. In a preferred embodiment, the volume in the barrel up to the barrier equals the fixed volume. The liquid measuring may further include a means to position the barrier to deliver a fixed volume of liquid, whereby the liquid can only be filled up to the barrier.
In a preferred embodiment, the liquid measuring device further includes a coupling device to adapt the barrier to the measuring device. In a more preferred embodiment, the coupling device includes an insert. In a most preferred embodiment, the insert is movable in the barrel. In another most preferred embodiment, the liquid measuring device further includes a holder to position and secure the insert in the liquid measuring device. In an alternate preferred embodiment, the insert is moved to a desired position by means of a screw.
In a preferred embodiment, the liquid measuring device is a pipette or syringe.
In a preferred embodiment, the liquid measuring device further includes a second barrel which is in fluid communication with said first barrel by means of a valve. In a preferred embodiment, the valve is a one-way valve. In an alternate preferred embodiment, the valve has an on/off switch.
In a preferred embodiment, the liquid measuring device may further include a needle at the distal end.
In a preferred embodiment, the insert of the liquid measuring device is H-shaped in cross-sectional view. In an alternate preferred embodiment, the insert is U-shaped in cross-sectional view.
In a preferred embodiment, the first barrel of the liquid measuring device includes a valve at the distal end. In a more preferred embodiment, the valve is a one-way valve. In an alternate more preferred embodiment, the valve is an on/off valve. In a preferred embodiment, the gas or vapor permeable but liquid impermeable barrier of the liquid measuring device comprises hydrophobic material.
The present disclosure also pertains to a method of measuring a fixed volume of liquid including the steps of:
1) providing a gas or vapor permeable but liquid impermeable barrier in a barrel having a proximal end and a distal end;
2) inserting the distal end into a sample comprising liquid fluid;
3) creating a negative pressure on the proximal end; and
4) transferring the liquid fluid from the sample into the barrel, wherein the liquid fluid can only be filled up to the barrier.
In a preferred embodiment, the method further includes adjusting the position of the barrier in the barrel. In a preferred embodiment, the barrier is part of a coupling device and the method further includes adapting the coupling device to the barrel. In a more preferred embodiment, the adapting includes inserting the coupling device into the barrel.
In a preferred embodiment, the barrel further includes a valve at the distal end and the method further includes opening and/or closing the valve.
In a preferred embodiment, the method further includes pulling a plunger in the barrier to create a negative pressure.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.